#include<stdio.h>
float printf_sum(float n)
{
    if(1==n)
        return 1;
    else
        return ((2*n-2)/(2*n-1))+printf_sum(n-1);
}
int main()
{
    float n=0;
    while(n<=0)
    {
        scanf("%f",&n);
    }
    printf("%.2f",printf_sum(n));
}